The invention relates generally to the field of calendars and, more particularly, to perpetual calendars.
Perpetual calendars are calendars that can be manipulated to display various different periods of time, such as weeks or months. Perpetual calendars are based upon the known yearly cycle of time as quantified by the months and days.
Many perpetual calendars function by aligning a day of the week, e.g., Monday, Tuesday, with the day on which January 1st of a given year falls. Once the day of the week on which January 1st falls in a given year is known, the dates and corresponding days of the weeks within that year are known based on the known number of days within a week and the dates in each month.
Year to year changes on the day of the week on which January 1st falls are taken into account based on the fixed number of days in a week and the known number of days in a year. While all weeks have seven days, the number of days in a year varies.
All years have 365 days, unless the year is a leap year, which has 366 days. A leap year is any year divisible by 4, except where the year is a century, e.g. 2000, 2100, which is only a leap year if also divisible by 400. Thus, the century 2000 was a leap year but the century 2100 will not be. The known number of days in a year combined with a fixed week of seven days mandates that January 1st of a year following a 365 day year begin on the next day of the week from which that year began. For example, if January 1st of a 365-day year was on a Monday, the January 1st of the following year will be on a Tuesday. In the special case where a year follows a leap year, the January 1st of the following year is not one day later but two, to account for the extra day in the 366-day year. For example, if January 1st of a 366-day year was on a Monday, January 1st of the following year will be on a Wednesday. The day of which January 1st falls in preceding years may be similarly obtained.
Over the years there have been many structures for perpetual calendars. Many of the calendars, however, do not simultaneously display the days, dates, months and year. Most display only a month with the days and dates therein. In addition, changing the relationship in the calendar to reflect for example months in a different year, particularly a leap year, is complex. Generally, most perpetual calendars make the assumption that a viewer of the calendar is only interested in the current month.
Based on the above, it is an object of the present invention to create a perpetual calendar that is more readily adaptable to changing the relationships depicted thereon.
It is another object of the present invention to create a perpetual calendar that more easily accommodates leap years.
It is still yet another object of the present invention to create a perpetual calendar that displays the entire relationship between the dates, days, months and years.
The present invention in one aspect is a perpetual calendar having a body with an outer surface. The outer surface is divided into seven segments, the number of segments corresponding to the number of days in a week. Date indicia for the longest month in a year, 31 indicia in all, are successively positioned on the outer surface in the seven segments. At least five-year indicia, representing a repeating pattern based on four years, are also positioned on the outer surface in each segment. The year indicia positioned in any one segment are based on the date indicia therein.
A cap is positioned relative the body and has an outer surface. Positioned on the outer surface of the cap are day indicia and month indicia. The day indicia and month indicia are positioned in a fixed relationship and define seven sections. The seven sections are consistent with the seven segments on the body such that a section aligns with a segment. The cap is positionable about the body permitting the seven sections to align with the seven segments to display a one month calendar for each aligned month and year. Preferably, the cap does not interfere with the viewing of the indicia of at least one month and corresponding year on the body, thus permitting the day, date, month and year to be simultaneously viewed.
The indicia within any segment or section can be arranged as desired therein. In addition, additional month ending indicia, indicia to indicate the last day of month, can be added to the segment having the day indicia that indicates the last day of a month. For example, xe2x80x9cAprxe2x80x9d can be added in the segment having day indicia 30 to indicate that April has 30 days.